1. Field of the Invention
The present invention relates to a drive unit for a hoisting apparatus according to the preamble of claim 1.
Spur gears, in particular planet gears, have recently been favored in such drive units over the worm gears formerly used almost exclusively, because they are more efficient and permit better performance, especially when starting up and slowing down.
2. Description of Related Art
A generic drive unit, known from WO 89/11436 A1, is of tripartite construction with a motor, a brake and a planet gear. The brake housing forms the supporting structure on which the motor and the planet gear are each flange-mounted. Due to the drive line with the series-connected components extending continuously in the axial direction, this unit has a comparatively great overall length which is sometimes excessive for the dimensions of an elevator shaft. Due to the unsupported planet gear flange-mounted on the brake housing and the loads of the cage and counterweight applied, a considerable pitching moment must also be taken up by the brake housing. Consequently, special measures must be taken with respect to the anchoring in the substructure of the building. Since the brake is positioned on the motor side, the toothing of the gearing is exposed to instantaneous loads, particularly during loading and unloading of the cage, so that premature wear must be expected.